This invention relates to the control of termites in relation to buildings and other structures and in particular to achieving such control without the use of harmful chemicals.
The most popular procedure for providing a barrier to the access of termites to buildings or other structures supported in or on the ground is to saturate the ground beneath or around the structure with appropriate chemicals, to kill any existing termites, and to provide a residue of the chemical within the ground which will remain effective for many years against the passage of termites therethrough to the structure. It has been proposed in published patent specifications to provide a mat of fibrous or absorbent material to be laid below the foundations of a building with the fibre or porous material saturated with, or containing an appropriate chemical which will kill termites that attempt to pass therethrough. Refer to published Australian Patent Application Nos. 85176/82, 11412/83, 16980/83 and 21934/84.
These methods of termite control have the major disadvantage as the chemicals are usually of a composition that is considered highly dangerous to humans and thus constitute a hazard to the people applying the chemicals and to other people in the vicinity. Under some atmospheric conditions, the chemicals can be carried considerable distances from the area where they are being applied. Thus people unaware of the presence of the chemicals, and thus not alerted to take protective action, may also be exposed to the potential danger of the chemicals used to control termites. The danger continues to exist after the initial application of the chemical so long as the chemical remains effective against the termites.
Also, as it is necessary to establish a high concentration of the chemical in the ground beneath where the building is to be built in order to obtain the required period of protection against termite entry to the building, leaching of the chemical will occur over time. This leaching will naturally reduce the effectiveness of the chemical as a barrier to the termites. As the chemical in many instances is initially placed beneath a concrete slab upon which the building is erected, it is very difficult to apply further chemical to replace that removed by the leaching and so maintain an effective barrier. Even more importantly, chemicals leached from the ground beneath the building are carried by the leaching water into other areas where it may be hazardous to humans, animals or crops. Also the leached chemical can enter rivers, streams or lakes or underground water catchments which can potentially spread the chemicals over a very wide area thus increasing the potential exposure to the chemical. It will also be appreciated that the chemicals leached from building sites over a relatively wide area can collect in a single river, stream or other catchment, thus resulting in an accumulation of chemicals that break down very slowly.
Many buildings, particularly homes, are built on a slab of concrete and although termites can normally not penetrate concrete, cracks frequently develop in the concrete thus permitting the passage of termites therethrough into the building. Even when the cracks are of a fine nature, they do provide the facility for the termites to burrow through the concrete by secreting materials which will break down the concrete along the fine cracks and thus permit the termites to burrow therethrough.
Also, in buildings erected on a concrete slab, it is common practice to provide pipes or conduits that extend through the concrete slab, such as water and waste pipes. As the concrete is cast in situ about these pipes or conduits, a small opening often develops about the pipe or conduit due to shrinkage of the concrete during curing.
These openings also provide access for termites through the concrete into the building structure. Thus even where a building is erected on a concrete slab, the ground beneath the slab must be treated with substantial quantities of chemicals to prevent access by termites to these openings.
It has also been known to use sheet metal as a barrier to termites such as galvanized steel plates on the top of stumps that support a building. Although this may be effective and commercially viable in relation to a building supported on stumps, it is expensive and has installation problems when considered in respect to a building supported on a concrete slab. Sheet metal is difficult to join on-site in a manner to exclude passage of termites through the joint. Also, if the metal sheet is sufficiently strong to prevent accidental puncture by workman traffic on-site, it is then difficult to bend and shape to the required contours to fit with the building structure in a manner to provide an effective termite barrier. It would also be difficult to achieve an effective seal around pipes or conduits that must pass through the sheet.
Sheet metal, including stainless steel, as proposed in French Patent Application No. 79 04240 (Publication No. 2453952) is used to provide a barrier to termites travelling up a wall to enter a building in a manner analogous to a metal plate on a building stump. However, that sheet is preformed for a specific installation and is not appropriate for on-site construction to a range of shapes and configuration with the ability to maintain the integrity of a barrier against the passage of termites.
In addition to buildings, termites attack a wide range of structures and equipment including wooden poles and other wooden structures, underground cables and conduits made of a range of materials that will be attractive to termites. The only effective protection for such structures are chemical treatment or solid metal barriers that are resistant to termite attack.
It is therefore the object of the present invention to provide a barrier that will inhibit the passage of termites such as into a building or structure, the barrier being both effective and avoids the use of chemicals that are harmful to humans and/or the environment.
With this object in view there is provided by the present invention an improved termite barrier which is substantially resistant to termite chewing and corrosion, the termite barrier comprising a mesh sheet formed of a material resistant to breakdown in the environment of use and substantially resistant to termite secretions, said material having a hardness of not less than about Shore D70 for resistance to termite chewing, the pores of the mesh having a linear dimension in any direction less than the maximum linear dimension of the cross section of the head of the species of termite to be controlled.
Conveniently the pores of the mesh having a linear dimension in at least one direction, less than the minimum lineal dimension of the cross section of the head of the species of termite to be controlled. Preferably, the pores in the mesh am polygonal with a maximum diagonal dimension less than the maximum linear dimension of the cross section of the head of the species of termite to be controlled.
Termites of the species which attack wood, timber or the like are characterised by having a head formed of a hard substantially nondeformable structure. The body of these termites is a relatively soft and weak material. Also these termites have a head which is of substantially larger cross sectional dimensions than any other part of their body. Accordingly the head cross sectional size determines the ability of the termite to pass through an opening or passageway such as may exist in any form of termite barrier.
It is also known that termites secrete a liquid saliva or material which is capable of breaking down the physical structure of many materials into at least particles of a size that can be transported by the termites so as to facilitate the formation of a passage for the termites to pass through. The secreted material includes, amongst other components, acids such as formic acid.
The mesh sheet can be laminated with a flexible plastic sheet or sandwiched between two separate sheets.
Alternatively the mesh may be embedded in one plastic sheet, preferably with both sides of the mesh sheet covered by the plastic material. The combining of the mesh sheet and the plastic provides protection of the mesh sheet against damage that may cause displacement of the strands forming the mesh, with resultant enlargement of the openings or pores of the mesh in a specific area thereof to a size to permit the passage of the termites therethrough.
It is also to be appreciated that it is normal practice to provide a sheet of plastic material beneath the concrete slab upon which a building is to be erected to provide a barrier against the entry of moisture through the concrete into the building. Accordingly, by incorporating the mesh sheet with or into a plastic sheet, the resulting assembly can perform the two functions of providing a moisture and a termite barrier.
In practical application of the termite material a continuous layer thereof is positioned beneath an underside of the slab extending to a perimeter of the slab in all directions and upwardly about the perimeter of the slab to a distance above the slab and above the ground level adjacent thereto.
Another application is in a building structure erected on a ground level or near ground level concrete slab, and having a non integral termite resistant adjacent structure and a strip of the termite barrier material arranged with the respective marginal edge portions along the opposite longitudinal edges of the strip integrally secured to the slab and the adjacent structure to establish integrity of the connection between the slab and the adjacent structure against the passage of termites.
Preferably the mesh is woven from fine stainless steel wire or filaments of the appropriate material, such as stainless steel, that is resistant to corrosion by most materials that the mesh will be in contact with or associated with during its use in the termite barrier. In particular, the stainless steel resists rust through contact with moisture, and resists attack by most acid materials, including formic acid and other constituents of the secretion released by termites. However, it is to be understood that wires, strands or filaments of other materials may be used to produce the mesh sheet provided the material has the required resistance to breakdown when exposed to the environment and materials present in the ground and to termite attack, and is sufficiently hard that the particular species of termites can not chew through the strands or filaments. Other materials may be fibres of ceramics, glass or hard plastics.
It is known that the physical dimensions of termites vary from species to species and that in different areas of the world, different species of termites are predominant. Accordingly, the actual size of the pores of the mesh will be determined by the particular termite or range of termites to be controlled in the particular area where the mesh is to be used.
In the area around Perth, Western Australia, the most common and dangerous termites are of the Coptotermes family which have a head of a generally circular cross sectional somewhat flattened shape, as shown in FIG. 2B with a maximum linear dimension of between 1 to 1.5 mm. It is thus suitable to use in that area a mesh having pores or openings having a maximum dimension in any direction of not more than 0.85 mm, and preferably not more than 0.6 mm. For convenience in manufacture, the pores will normally be of a generally rectangular shape with the length of the sides 0.4 and 0.7 mm respectively.
The wire of filament may be of any convenient commercial size and typically may be in the range of 0.1 to 0.2 mm in diameter. The wire of filament may be of cross-section is preferred and more readily commercially available in the manufacture of mesh. The mesh may also be produced by stamping or punching holes of the required shape in sheet or film of metal or other suitable material of an appropriate thickness.
In most species of termites there are worker termites and soldier termites, the latter having larger heads than the worker termites in some species, but not all. It is thought to be normal for the soldier termites to lead or at least travel with the invention. Thus it is believed that if the mesh has pores of a size to prevent the passage of the soldier termites, this would be effective in inhibiting the worker termites from passing alone through the mesh. The workers are the ones that cause the damage and must be stopped by the mesh.
The plastic material forming the sheet with which the mesh sheet can be laminated or embedded in, is conveniently PVC, but may be of any other suitable plastic which will provide a moisture barrier and will not deteriorate and break down when buried in the ground for the normal life expectancy of termite barriers which may be of the order of 15 to 30 years.
Conveniently, the termite barrier is produced in sheets of any convenient size and may be produced in a form of roll of a width of the order of 5 to 10 meters.
The advantages of the termite barrier as proposed above are principally that there are no harmful chemicals used in the creation of the barrier, the barrier will have an effective life commensurate with the life of the building. Further, the barrier can be conveniently transported and applied without the level of precautions required when handling pesticides or other chemicals and with a minimum of skill. Further as the barrier is in the form of a mesh, it is substantially more flexible and easily worked as by cutting, contouring and shaping, particularly in comparison with solid sheet metal.